Impact tools



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Aug. 30, 1955 w. G. MITCHELL 2,716,475L

IMPACT TOOLS Original Filed March 17, 1949 2 Sheets-Sheet 2 UnitedStates Patent "O IMPACT TOOLS Walter G. Mitchell, Aurora, Ill., assignorto Thor Power Tool Company, Aurora, Ill., a corporation of DelawareOriginal application March 17, 1949, Serial No. 81,966, now Patent No.2,585,486, -dated February 12, 1952. Divided and this applicationSeptember 7, 1951, Serial No. 245,526

Claims. (Cl. 192 30.5)

This application is a division of my copending application Serial No.81,966, tiled March 17, 1949, now Patent 2,585,486, issued February 12,1952.

This invention relates to improvements in portable power operated impacttools for setting and removing nuts and bolts by power, and moreparticularly to improvements in an impact clutch mechanism employed insuch impact tools for clutching and declutching the hammer and anvilmembers and for imparting rotational hammer blows on the anvil member totighten or loosen anut or bolt.

In my copending parent application Serial No. 81,966, I have describedand claimed various novel features of my invention and more particularlyan impact clutch mechanism comprising a novel arrangement of a pair ofrotatable hammer and anvil members, impact means, and

actuating means for the impact means. The present divisional applicationis directed more specifically to a novel arrangement of a pair ofrotatable hammer and anvil members with a supporting shaft whereby topermit limited angular or cocking movement of the anvil member relativeto the shaft.

Accordingly, the primary object of my invention is to provide an impactclutch mechanism having novel means for avoiding the inherent tendencyof the anvil member of the device toward binding due to misalignment onthe drive shaft during operation of the tool.

A further object of the invention is to provide in an impact clutchmechanism a novel combination of axially disposed rotatable anvil andhammer members and a supporting shaft with means for permitting limitedangular or cocking movement of the anvil member relative to the shaftduring operation of the tool.

Other and further objects and advantages of the present invention willbecome apparent hereinafter as the description progresses, referencebeing had to the accompanying drawings in which: y

Fig. l is a longitudinal sectional view with portions thereof inelevation and showing an impact tool comprising a preferred embodimentof the present invention;

Fig. 2 is a fragmentary longitudinal sectional view of the impact tooltaken on the line 2-2 in Fig. 1;

Fig. 3 is a transverse sectional view taken on the line 3 3 in Fig. 1;

Fig. 4 is a transverse sectional view taken on the line 4 4 in Fig. l;

Fig. 5 is a transverse sectional view taken on the line 5 5 in Fig. 1;

Fig. 6 is a transverse sectional View taken on the line 6 6 in Fig. l;and

Fig. 7 is a perspective View of the impact unit and gear drive of thetool, showing the hammer in aligned but disassembled position withrespect to the spindle and impact rods or jaws.

Referring now to the drawings, the impact tool illustrated thereincomprises a four section housing including an impact unit section at theforward portion of the 2,716,475 Patented Aug" 30, 1955 tool, a gearsection 20a at the intermediate portion thereof, a eld case 21containing an electric motor, not shown, and a cap 22 at the rear endthereof. As more fully described in my earlier application Serial No.81,966, the field case 21 is provided at its rearward end withsupporting structure for a ball bearing unit having journaled thereinthe rear end of an armature shaft 26. A motor reversing ring 28, whichmay be composed of plastic or other suitable material, abuts the extremerearward end of the housing section 21 and is held in positionthereagainst for limited rotative movement by the cap y22. As explainedmore fully in my earlier application, relative rotative movement of theplastic ring 28 in one direction or the other serves to reverse theoperational direction of the motor contained in the housing section 21.The armature shaft 26 is journaled on its forward side in a ball bearingunit 37 supported within a bushing 38 which is secured within the axialopening of an annular, cupshaped cross portion 39 extending diagonallyinwardly and rearwardly from the forward end of the housing section 20a.

Rotary motion of the electric motor contained in the housing section 21is transmitted to the impact unit within the forward housing section 20by means of a planetary gear train. The forward end of the armatureshaft 26 is shaped to provide a gear 46 in constant mesh with a pair ofdiametrically opposed, planetary gears 47 mounted for free rotativemovement on short shafts 48 secured in a spider member 49. The spidermember 49 isintegrally formed as the upper or rearward end portion of adrive shaft 50 and its extreme rearward end is journaled for freerotative movement in a thrust ball bearing unit 51 also received in thebushing 38. The planetary gears 47 are also in constant mesh with aninternal ring gear 52 secured in and projecting somewhat beyond theextreme forward open end of the housing section 20a. The ring gear 52 isprovided with an outwardly directed annular shoulder 53 which forms aseat against which the rearward end of the impact housing section 20 maybe drawn up into tight engagement by means of suitable screws, as shownmore fully in my copending application Serial No. 81,966. By thisarrangement the assembly and disassembly of the tool is greatlyfacilitated. The entire front end of the tool including the impactmechanism, its housing section 20, the drive shaft 50, the spider 49,the planetary gears 47 and the ball bearing unit 51 may be withdrawn orseparated as a unit from the rear portion of the tool merely by removingthe screws and sliding the planetary gears 47 relative` to the pinion 46and the ring gear 52 out of meshing engagement therewith. As will becomeapparent hereinafter, the impact mechanism may then be removedrearwardly out of the housing section 20. v

The forward end of the drive shaft 50, comprising the main supportingmember` or stern of the impact unit, is received within an axial bore 54of an impact spindle or anvil 56 which terminates in a square section 57exteriorly of the housing section 20 and is adapted to mount and drive anut or bolt engaging socket (not shown) in the f usual manner. Theimpact spindle 56 is adapted to rotate within a bushing 58 secured by aset screw 59 within the vaxial opening at the forward end of the housingsection 20. A rotatable hammer member 60 is mounted on the drive shaft50 above the impact spindle 56 for free and independent rotativemovement relative thereto, the hammer 60 being provided with an axiallyextending central opening in which is secured a needle bearing 61facilitating rotative movement between the parts. A thrust washer 62 isalso mounted on the shaft 50 between the hammer and the impact spindle56.

The hammer 60 is provided with longitudinally extending openings 63 ondiametrically opposite sides of the central axial opening 55, theopenings 55 and 63 thus being parallel and in alignment, and the hammer60 thus being of solid, rugged construction and possessing great massand inherently great strength. A pair of impacting rods or jaws 64 areslidably mounted within and extend through the hammer openings 63, thelower ends of the rods 64 being adapted to project when in impactingposition, as shown in Figs. l and 3, beyond the forward end surface ofthe hammer 60 and into arcuate slotted openings 66 in a radiallyoutwardly directed anged portion 67 of the anvil 56. As will beexplained in detail hereinafter, 'the impact rods 64 rotate with thehammer 60 and are adapted to strike the anvil 56 at the abutments formedby thev ends of the arcuate slots 66 to cause rotation of the anvil.

The upper ends of the impact rods 64 are each provided with an annulargroove 68 into which are received the edges of bifurcated portions 69extending radially from the forward end of an arched cam lifter plate70. The

`impact rods 64 may be readily mounted on the cam lifter plate 70 bysliding them inwardly into the slots 65 thereof from the outer edges ofthe bifurcated portions 69 and they are then free to rotate relativethereof. The cam lifter plate 70 is provided with a central axialopening through which the drive shaft 50 extends, the plate 70 beingslidable on the shaft 50 for axial movement relative thereto. Arelatively heavy compression spring 71 encireles the cam plate 70 andthe forward end thereof seats against the radial edge portions of thebifurcated portions 69 outwardly of the heads of the impact rods 64. Bythis arrangement the carn plate 70 is constantly urged for wardly so asto project the impact rods 60 into impact* ing position. The spring 71also serves the further purpose of retaiping the impact rods 60 inassembled position within the slots 65 of the bifurcated portions 69during assembly of the various parts of the tool and permits the impactmechanism to be assembled and handled as an integral unit.

The upper end of the compression spring 71 bears and seats againstradially directed flanges 72 of an upper spring plate 73, this plate 73also being slidable on the drive shaft S and being separated from theforward endl surface of the spider member 49 by thrust bearings 74. Theupper spring plate 73 is attened around the shaft S0 on the forward sidethereof to provide -a surface 76 for engagement with a hat cooperatingsurface 77 on the rearward end of the cam lifter plate 70, the surface77 being adapted to be moved upwardly into such engagement upon extremerearward movement of the lift plate 70.

On the forward or under side of the cam lifter plate 70 are twoprojecting cam members 78, one on each side of the drive shaft 50, whichare forced forwardly into constant bearing engagement with cam surfaces79 on a -drive cam member or bushing 80 iixed on the drive shaft 50 forrotation therewith and restrained against axial movement relativethereto. The cam surfaces 79 slope upwardly in either direction from thelow point thereof thus enabling the tool to be operated in a reversiblemanner in either direction of rotation. The cam bushing 80 is secured onthe shaft 50iby means of balls 81 disposed within aligned andcooperating openings 82 and 83 in the bushing 80 and the drive shaft5i), respectively. The forward end of the cam bushing 80 is receivedwithin an annular recess 84 in the rearward end of the hammer 60 andbears against a thrust washer 86 at the back of the recess.

As shown clearly in Figs. 2, 5, and 7 of the drawings, the hammer 60 isprovided with two diametrically opposed and aligned ears or projections87 which extend rearwardly in parallel relationship up within the spring71 and on each of the opposite sides of the cam bushing 80, the camlifter plate 70 and its cam portions 78. The outer peripheries of thehammer ears 87 are curved so as to conform to the curvature of thespring coils but they are spaced therefrom to permit free relativemovement between the spring 71 and the hammer 60. The inner surfaces ofthe hammer ears 87 are smooth, at and parallel with each other andparallel with the drive shaft 50, and are in close, slidable engagementwith the smooth, flattened surfaces 88 on the opposite sides of the camlifter plate 70.

The hammer ears 87 thus serve to maintain the parts of the impact unitin perfect alignment and insure perfect alignment of the slots of thebifurcated portions 69 of the cam lifter plate with the axial hammeropenings 63. As a consequence, the impact rods 64 are always maintainedin perfect and absolute alignment within the hammer openings 63 for freerelative slidable axial movement to and from impacting position. Sincethe parallel inner surfaces of the hammer ears are parallel with theaxial openings 63 of the hammer 60 and bear against the opposite flatvparallel surfaces of the cam lifter plate 70, absolute parallelismbetween the parts is maintained at all. times. Any forces tending torotate the hammer 60 in one direction relative to impact rods 64 so asto tend to effect their disalignment and to cause the rods to bearagainst one side of the hammer slots 63, also, through the hammer ears87, tend to rotate the rodcarrying cam lifter plate 70 in the samedirection and with equal force, thus preventing any such disalignment orbinding engagement. lt is to be noted that the opposite longitudinalside edges of the cam portions 78 of the cam lifter plate extendslightly beyond the outer periphery of the driving cam bushing so thatthe cam bushing 80 is out of engagement with inner surfaces of thehammer ears 87. The hammer ears 87 also guide the cam lifter plate 70 ina true axial direction when it is cammed upwardly by the cam bushing 80and serve to restrain the plate 70 against rotative movement.

On the under side of the housing section 21 is a switch grip handle 89having a trigger block 94 slidably received within an opening in thefront of the handle and adapted to cooperate with a switch device withinthe handle for closing and opening the electric circuit to the motor, asdescribed in detail in my earlier application 'Serial No. 81,966. Thetrigger block 94 may be held in its inward position for continuousoperation of the tool by a spring pressed locking plunger 112 extendingthrough the forward portion of the handle and may be quickly unlocked bydepressing and releasing the trigger block94.

When a nut or bolt is to `be tightened, the operator first places thesocket (not shown), secured on the square 57, over a nut or bolt headand then presses the .trigger block 94 inwardly to complete the electriccircuit and effect operation of the tool motor. As the armature shaft Z6rotates, the pinion gear 46 on its forward end rotates theplanetarygears 47, causing them to move bodily around within the ring gear 52 ina counterclockwise directio`n as viewed in Fig. 6 and thus causingrotation oi `the spider 49 and the drive shaft 50. This driving torqueis further transmitted to the impact rods 64 andthe hammer 60 throughthe cam bushing 80 .and the kcam .lifter plate 70.

At the outset of the tightening operation, the impact rods 64 aremaintained in projected position within the slots 66 of the impactspindle 56, as shown lin Figs. l and 3, and abut against the respectiveends thereof so as to rotate the impact spindle 56 and the socket andtighten the nut or bolt. As long as the nut or-bolt is Vrelatively frecrunning, the impact rods 64 remain vin-censtant engagement with theimpact spindle 56 and -the projecting cam Vportions 78 of the cam lifterplate 70 are disposed at the low points of the cam faces 79 of thebushing 80. However, when the nut or 'bolt .approaches tightenedposition and resistance to rotation is. suflcient to `over- .come thedriving ltorque of the tool motor and the exbushing 80 continue torotate under the driving force of the motor '29, the'camlifterrplateif70iwilllbefcmmc'd rearwardly in avstraig'ht-longitudinalor axial directionunderthe guiding'inuenceof-the hammer ears 87. f' Since the cam lifterplate 70 carrieszand supportsI the impact rods 64, these rods l also aremoved :rearwardly lrelative tothe hammer A60 andtheyare thus.withdrawnifrom the slots.66 to apoint slightly above :they rearwardsurface of the then stationary impact'spindle 56. Whenitheiimp'act rods64 are fully .withdrawn the .projecting cam-members 78 .of the cam'lifter plate .7.0 engage lthetcam-sur- .faces 79 of the bushing80 nearthe top of their `high points.

.In this withdrawn rearward position, the .impactrods 64 are out ofdriving engagement :with the impact .spindle 56 and hence are free torotate under the drivingtorque of the drive shaft 50. .The-impact rods64 and .the 'ha'mmer 60, consequently,v resume Erotation in a clockwiseVor tightening direction, passover. the narrow'landsbetween theimpactspindleslots' 6,6.;and-.then are projected under the .urge of thespring 71 back.into theslots-66 `so that .the impact rods 6 4 will be.impactedragainstthe farA end of the slots 66 -uponcontinued rotation.From thetime that driving engagement is broken'oifjasfabove'described,until-the rods 64 impactagainstthe .ends1of `theslots V66, thedriveshaft 50 accelerates `underfthe -dr'iving force fof the motor 29 at anvever increasing rate-so `that theimpact rods 64 strike the impactispindle 56 .with great force. Because of the solidmassive constructionof..the'ham mer 60, this impacting-force `is of relatively greatmagnitude. Y 2 t Because of the fact that the impact :rods f64arecircular and are slidably received in the. slots -:65..of `the camlifter plate 70, theyare free torotate relativegthereto. Asa result ofthis-rotative connection, the frods f64.a`re rotated slightly as theyare.v moving vinto impacting posi- Cil tion against the far ends ofthe.slots,66, thus-,presenting diierent circumferential :portions of-the lower `or blowdelivering ends of the rods tothe slotabu'tments :foreach blow. The rods, therefore, present new wearingsurfaces and have along operable life. f

.It is to be noted further that `when thedriving' `engagement isinitially brokenolf between the impact -vrodsI 64 `andthe impact spindle56, thecam portion 78fofrthecam lifter plate 70 engages Vthecam-bushing-B-near the high point on its cam surface. Consequently, asimpact rods 64 again accelerate toward impacting engagement with theimpacting spindle 56, the kheavy spring 71 will 'force .the cam lifterplate 70 axially forwardly, `the cam ,portion 78 moving downwardly andforwardly over the cam surface of the cam bushing.80toward its lowpoint. The cam lifter plate 70 is thuscaused to accelerate aheadef thedrive shaft 50 and the impact rods-64 are caused-to strikethe impactingspindle-56 with-an increased impacting force and at a rate -of rotationover andv above that of the drive shaft 50. Afterimpact, which causesfurther mer slots 63, the sliding movement of the rods 64 is alsoparallel `therewith; Consequently, itis vapparent that by thearrangement of the parts they are maintained in the desired alignment sothat their free operation'iis achieved at all times and no binding ofthe rods 64 inthe hammer slots 63 results. v 1 v When it is desired toutilize the tool for the purpose of loosening a nut or bolt, theoperator need only l,rotate the plastic reversing ring 28 to its-otherpositionas above described, and .the electric motor will thus operatelin the reverse direction and the drive shaft 550 will also be rotatedin the reverse direction. Since the work is in a tightened state, ztheimpact rods 64 will immediately commence imparting blows against thespindle 56 until the resistance-to rotation offered by thework `is lessthan the-driving torque of the cam lifter plate `70, at which point theimpacting blows cease and the impact rods l64 l remain in constant freerunning engagement' with the impact spindle 56. The toolmay-then'beallowed `to remain in engagement with the work until the work isentirely disengaged from a threaded opening.

Having thus described the general .mode vof operation of a rotary powertool utilizing an impact clutch mechanism-of the type illustrated,.Iwill now describe the specific improvement to which the presentapplication is particularly directed. It will be understood that thespecific features hereinafter described are broadly applicablev tovarious impact clutch arrangements other than those involving thespecific impacting and actuating means described above.

As shownrmore particularly in Figs. `l yand 2 of the drawing, the loweror forward end portion of the drive shaft is constructed so as 'topermit limited tilting or cocking movement of the impacting spindle oranvilv56 relative to the drive shaft 50. When the tool is in .opera-`tive engagementwith the work and is in the hands of an fop'era'tor, theimpacting forces and the handling of y the Etool bythe operator tend toforce the impacting spindle -56 .out vof alignment with the drive shaft5 0. --Because fof this' inherent tendency toward misalignment which;wou`ld cause binding'of the impact spindle56 if 4there, was

a1tightfit lbetween the parts and hence would `reduce the effectiveoutput of the -driven shaft `50 `and the spindle -56 .the extremeforward end of the -driven shaft V50'=is rounded ortaperedas'at 13'4leaving avreduced lilat end face ',136 for abutting engagement with :athrust washer annular-.bearing surface 139 which is adapted to engagelimited rotative and tightening movement ofithe impact spindle 56, theimpact rods 64-are againwithdrawn .as above described and are againrotated relativeato the-irnpact spindle 56 and thrown againintofimpactingrengagement with the spindle 56 at the far ends of thenext succeeding slots 66. The :impactfrods 641thus'strike the impactspindle 56 two impactingblowsfor every revolution of the hammer 60 andthese blows maybe repeateduntil the work has been. tightened toi-thedesired degree. A'

'During the operation-of lthe tool when the impacting blows are .being.delivered to thewoi'ln the impact vrods v64 are freely slidablewithin-'the hammer slots `6'3't`o and from spindle engaging positionsince they are maintained in perfect alignment therewith by the hammerears 87 which engage the ilat sides 88 of the cam lifter plate 70. Thehammer ears 87 also by their slidable engagement with the flat sides ofthe cam lifter plate 70 cause that plate to move in a truly longitudinaldirection and parallel to the inner sides of the hammer ears. Since theinner sides of the hammer ears 87 are also parallel with the ham- ;thewalls of-the yspindle bore 54overa limited area. This limited .bearingsurface 139 serves to .prevent too .loose J,a mounting between. thespindle 56 and theshaft 50 but .at the same time permits limited tiltingmovement therebetween. The forward and inward edges of the bearingsurface 139 wear away or round off after a relatively short :periodoftooloperation so thatthis bearing surface, as the .tool wears in andthe parts adjust themselves vto eachother, also becomes slightly roundedtothe desired .degree n i' v,'lheportionof the drive shaft 50 nextaboveor rearwardlyv'ofithe bearing surface 139.is of reduced diameter,as indicated at 140, and is slightly spaced from the sides ofthe spindle.bore 54 and the thrust washer 62 to provide aclearance `141 for thelimited tilting movement. The "diameteriof the drive-shaft portionindicated at 142 within the central bore 5S of the hammer 60 is also oflesser extent than the diameter of that bore so as to provide clearancetherebetween, and the needle bearing 61 serves to maintain the properbearing relationship between the hammer 60 and the drive shaft 50. Alsofor the purpose of permitting the relative tiltingmovement, the marginalor radially outer portion of the annular flanges 67 of the v impactspindle 56 are cut away so as not to extend rearmaeva wardly as far asthe central portion thereof, thus providing a slight clearance`143between the opposed end faces of the hammer 60 and the spindle 56 attheir outer portions and for engagement therebetween and with the thrustwasher 62 only at their central portions around the drive shaft 50.

Thus, by reason of the special construction of the shaft and the pair ofanvil and hammer members thereon, the clearances indicated at 141 and143 are provided so that the anvil or spindle 56 can undergo limitedcooking movement or axial misalignment without binding and therebyfacilitating easy operation of the tool. v

It is to be further understood that while the preferred embodiment ofthe present invention has been described above as an impact wrench, thevery same tool by means of special attachments secured on the square 57may be adapted for other uses such as a screw driver, tapper, reamer,drill, sander, polisher or wire brush driver. When utilized for theselatter purposes, the tool will be primarily free running withoutoperation as an impacting wrench. However, such impacting features arepermitted to become elective when used as a screw driver or when used asa drill and the drills or bits become Jfrictionally held againstrotation before the drill hole has been completed. The impacting blowsof the hammer rods 64 then are applied to the drills and bits toovercome such frictional resistance and any overload on the motor iseliminated. Although there has been described above and illustrated inthe drawings a preferred embodiment of an impact tool comprising thepresent invention, it is apparent that modifications and changes may bemade in the details of structure .and mode of operation withontdepartingfrom the spirit and scope of the appended claims.

lclaim:

T? An impact clutch comprising relatively rotatable axially alignedhammer and anvil members having aligned axial bores therein and analigning shaft in said hammer bore supporting said hammer for rotatablemovement thereon and extending into the bore of said anvil for rotativemovement relative thereto, the portion of the shaft within said anvilbore being of lesser diameter and spaced from the walls of said borealong a major portion of vits extent and having a generally cylindricalenlargement of relatively short axial extent in bearing engagement withthe walls-of said bore whereby said anvil and hammer members maymoveangularly out lot axial alignment to a limited extent withoutinterference lwith free relative rotation.

2. An `impact clutch comprising relatively rotatable axially alignedhammer and anvil members having aligned axial bores therein and analigning shaft in said hammer bore supporting said hammer for rotatablemovement thereon and having a free end extending into the bore of saidanvil for rotative movement relative thereto, the portion of the shaftwithin said anvilbore being of lesser diameter and spaced from the wallsof vsaid bore along a major portion of its extent and having adjacentthe free end thereof a generally cylindrical enlargement of relativelyshort axial extent in bearing engagementjwith the walls of said borewhereby said anvil and hammer members may move angularly out of axialalignment to a limited extent without interference with free relativerotation. j

3. An impact clutch comprising relatively rotatable axially alignedhammer and anvil members` having aligned axial` bores thereingand analigning shaft in said hammer bore supporting said .hammer for rotatablemovement thereon and havingI a free end extending into the bore of saidanvil for; rotative movement relative thereto, the portion of the`-shaft .within said anvil bore being of lesser diameter and spaced fromthe walls of said bore along a major portion of iitsextent and havingits freeend rounded' and having a generally cylindrical enlargement ofrelatively short axial extent adjacent said rounded end in bearingengagement with the Walls of said bore whereby said anvil. and hammermembers may move angularly. out-of axial alignment .to a limited extentwithoutinterferencewith free relative'rotation. 4.- Aniv impactlclutch.comprisingV relatively rotatable axially aligned hammerf andianvilmembers having aligned .axial bores ltherein and: having' axiallyopposed wall portionswith abutments on' the axially opposed wall portionof the anvil member,k impact means rotatably movablewith said hammer andaxially movable independently of saidihammerinto-an'd out of the path ofthe abutments for. clutching-,and declutchingsaid members and forimparting rotational hammer blows on the anvil member at said abutments,anda driving shaft-in ysaidhammer bore supporting said hammerfor-rotatable movement therein and having a lfree Vend extending intothe bore of said anvil forrotative movement relative-thereto, theportionof-,the shaft-within,` said anvil'bore being of lesserdiameterand spaced from the walls of said bore along a major portion ofits extent and having a generally cylindrical enlargement vofrelatively' short 'axial' extent in bearingengagement withthe Walls ofsaid bore,-and said hammer vand anvil members being-n bearing engagementwith each .other atftheir central axial portions and being axiallykspaced from each other at'their outer portions whereby said Vanvil andhammer members may move angularly out of axial alignment to a limitedextent durlng operation thereof-'without interferencewith free re1-ativeirotation.

5. In. an impact clutchj'a' rotatable hammer member havingA anpaxial-bore therethrough, a rotatable anvil memberhaving van laxial recess inalignmentl with said bore, and av'shaft extending through said bore'andhaving an `end-.portionextending into said'recess, said end portronbeing provided adjacent its kvouter extremity with/agenerally'cylindrical enlarged bearing portion of relatively shortaxiallext'ent substantiallyless than the axial depth of said recess anddisposed in bearing engagement with the wall of said recess for normallyretaining the hammer and anvilv members in axial ialignment, theremainder of said-end portion inwardly of saidfbearing portion being ofreduced diameter relative to said recess whereby to provide -an annular'clearance therebetween, and said hammer and anvil members havingtheiropposed endsaxially spaced from each other adjacent the outerperipheries thereof, whereby to permit limited angular displacement ofsaid anvil member relative'to said shaft and said hammer member' withoutinterference with .relative rotary movement of theparts. i

References Cited in the file of this patent STATES PATENTS 1,871,227.smith etal. An 9 1932 75,004V Behr 1 Ma 3I 1942 ,j 33,703 .,wilh'de eta1. D l 2,564,224 ec. 12, 1950 Mitchell et al. Aug..14, 1951

